Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$26.30	8.226%	$28.4634	$28.46	$28.45	$28.50
Purchase #2	$105.51	11.380%	$117.517	$117.52	$117.50	$117.50
Purchase #3	$69.28	3.647%	$71.8066	$71.81	$71.80	$71.80
Purchase #4	$30.46	11.129%	$33.8499	$33.85	$33.85	$33.80
Purchase #5	$156.74	7.428%	$168.3826	$168.38	$168.40	$168.40
Purchase #6	$75.31	7.745%	$81.1428	$81.14	$81.15	$81.10
Purchase #7	$185.53	12.335%	$208.4151	$208.42	$208.40	$208.40
7 purchase totals =	$649.13		$709.5774	$709.58	$709.55	$709.50